Physical processes in ice-covered Lake Vendyurskoe were studied during December 1998 - April 1999 and December 1999 - April 2000. Temperature and salt concentrations were recorded using thermistor chains moored beneath the ice and temperature-conductivity-depth profilers. The flux of solar radiation at the ice-water interface was measured. For the first time, measurements of the small-scale temperature fluctuations in the convective layer beneath the ice were performed with a microstructure profiler. The collected data were used together with data from previous field studies in Lake Vendyurskoe and other ice-covered lakes in the vicinity to analyse the structure and the evolution of the temperature and salinity fields, and to develop parameterisations of heat and mass transport in ice-covered lakes. Dissipation rates of turbulent kinetic energy and of the temperature variance have been determined.

A new parameterisation of the temperature profile in the bottom sediments and of the heat and mass fluxes across the water-bottom sediments interface was developed. The parameterisation was included into a column model of seasonal temperature changes and mixing conditions in lakes (TEMIX). Simulations with the upgraded TEMIX model show a better agreement between simulated and observed temperature fields for the period of ice cover than previous approaches. Detailed description of the interaction between sediments and water is essential for understanding mixing and for how lake ecosystems function during winter.

The turbulence structure and transport properties of penetrative convection driven by the vertically distributed radiation heating is analysed through large-eddy simulation (LES). Such convection occurs in ice-covered lakes in late spring, when the snow overlying the ice vanishes and the solar radiation penetrates down through the ice. Simulations of the dissipation rates of turbulent kinetic energy and of the temperature variance were compared with the microstructure measurements. Using the arguments behind the Deardorff scaling, scaling was proposed for the convection driven by the radiative heating. A mixed-layer model of convection under the ice was developed and applied to simulate the mixed layer deepening. The model utilises a stationary solution to the heat transfer equation to describe the structure of the stably stratified layer beneath the ice, a four-layer self-similar representation to parameterise the evolving temperature profile, and the proposed mixed-layer scaling to derive the entrainment equation. Good agreement is found between simulations and observations. Knowledge of the turbulence structure and transport properties of convection under the ice helps to understand and quantify chemical and biological processes in lakes. Convective motions suspend non-mobile phytoplankton species in the surface layer, thus leading to their growth.

References

Golosov, S., I. Zverev, and A. Terzhevik, 2000: Modelling thermal structure and heat interaction between water column and bottom sediments. (In preparation. Preliminary results are given in Report No. 3250 [LUTVDG/(TVVR-3220) 1-41/(1998)] available from the Department of Water Resources Engineering, Inst. of Technology, Univ. of Lund, Lund, Sweden, 41 pp.).
Jonas, T., A. Terzhevik, D. Mironov, and A. Wuest, 2000: Investigation of radiatively-driven convection in an ice-covered lake using temperature microstructure technique. J. Geophys. Res., 108(C6), 3183, doi:10.1029/2002JC001316.
Kirillin, G., D. Mironov, and A. Terzhevik, 2001: Radiatively-driven spring convection in ice-covered lakes: the effect of salt concentration, Abstract sent to Physical Processes in Natural Waters, 6th Workshop on physical processes in natural waters, X.Casamitjiana(ed.), 199-203, Girona, 2001.
Mironov, D., S. Danilov, and D. Olbers, 2001: Large-Eddy Simulation of Radiatively-Driven Convection in Ice-Covered Lakes, Abstract sent to Physical Processes in Natural Waters, 6th Workshop on physical processes in natural waters, X.Casamitjiana(ed.), Girona, 2001.
Mironov, D., A. Terzhevik, G. Kirillin, T. Jonas, J. Malm, and D. Farmer, 2001: Radiatively-driven convection in ice-covered lakes: observations, scaling and a mixed-layer model. J. Geophys. Res., 107, No. C4, 7-1-7-16.
Mironov, D. V., and A. Yu. Terzhevik, 2000: Spring convection in ice-covered fresh-water lakes. Izv. Rus. Acad. Sci. Atmos. and Oceanic Phys., 36, 627-634.
Terzhevik A. Yu., Boyarinov P. M., Filatov N. N., Mitrokhov A. V., Palshin N. I., Petrov M. P., Jonas T., Schurter M., Maher O. Ali, 2000: Field study of winter hydrodynamics in Lake Vendyurskoe (Russia), Abstract sent to Physical Processes in Natural Waters, 5th Workshop, 110-113, Irkutsk, Russia, 2000.